/*
   Copyright (C) 2005 John McCutchan

   The Gnome Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The Gnome Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the Gnome Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.

   Authors:.
		John McCutchan <john@johnmccutchan.com>
*/

#include "config.h"

#include <stdio.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <glib.h>
#include "inotify-kernel.h"
#include <sys/inotify.h>

/* Timings for pairing MOVED_TO / MOVED_FROM events */
#define PROCESS_EVENTS_TIME 1000 /* milliseconds (1 hz) */
#define DEFAULT_HOLD_UNTIL_TIME 0 /* 0 millisecond */
#define MOVE_HOLD_UNTIL_TIME 0 /* 0 milliseconds */

static int inotify_instance_fd = -1;
static GQueue *events_to_process = NULL;
static GQueue *event_queue = NULL;
static GHashTable * cookie_hash = NULL;
static GIOChannel *inotify_read_ioc;
static GPollFD ik_poll_fd;
static gboolean ik_poll_fd_enabled = TRUE;
static void (*user_cb)(ik_event_t *event);

static gboolean ik_read_callback (gpointer user_data);
static gboolean ik_process_eq_callback (gpointer user_data);

static guint32 ik_move_matches = 0;
static guint32 ik_move_misses = 0;

static gboolean process_eq_running = FALSE;

/* We use the lock from inotify-helper.c
 *
 * There are two places that we take this lock
 *
 * 1) In ik_read_callback
 *
 * 2) ik_process_eq_callback.
 *
 *
 * The rest of locking is taken care of in inotify-helper.c
 */
G_LOCK_EXTERN (inotify_lock);

typedef struct ik_event_internal {
	ik_event_t *event;
	gboolean seen;
	gboolean sent;
	GTimeVal hold_until;
	struct ik_event_internal *pair;
} ik_event_internal_t;

/* In order to perform non-sleeping inotify event chunking we need
 * a custom GSource
 */
static gboolean
ik_source_prepare (GSource *source,
				 gint *timeout)
{
	return FALSE;
}

static gboolean
ik_source_timeout (gpointer data)
{
	GSource *source = (GSource *)data;

	/* Re-active the PollFD */
	g_source_add_poll (source, &ik_poll_fd);
	g_source_unref (source);
	ik_poll_fd_enabled = TRUE;

	return FALSE;
}

#define MAX_PENDING_COUNT 2
#define PENDING_THRESHOLD(qsize) ((qsize) >> 1)
#define PENDING_MARGINAL_COST(p) ((unsigned int)(1 << (p)))
#define MAX_QUEUED_EVENTS 2048
#define AVERAGE_EVENT_SIZE sizeof (struct inotify_event) + 16
#define TIMEOUT_MILLISECONDS 10
static gboolean
ik_source_check (GSource *source)
{
	static int prev_pending = 0, pending_count = 0;

	/* We already disabled the PollFD or
	 * nothing to be read from inotify */
	if (!ik_poll_fd_enabled || !(ik_poll_fd.revents & G_IO_IN))
	{
		return FALSE;
	}

	if (pending_count < MAX_PENDING_COUNT) {
		unsigned int pending;

		if (ioctl (inotify_instance_fd, FIONREAD, &pending) == -1)
			goto do_read;

		pending /= AVERAGE_EVENT_SIZE;

		/* Don't wait if the number of pending events is too close
		* to the maximum queue size.
		*/
		if (pending > PENDING_THRESHOLD (MAX_QUEUED_EVENTS))
			goto do_read;

		/* With each successive iteration, the minimum rate for
		* further sleep doubles. */
		if (pending-prev_pending < PENDING_MARGINAL_COST(pending_count))
			goto do_read;

		prev_pending = pending;
		pending_count++;

		/* We are going to wait to read the events: */

		/* Remove the PollFD from the source */
		g_source_remove_poll (source, &ik_poll_fd);
		/* To avoid threading issues we need to flag that we've done that */
		ik_poll_fd_enabled = FALSE;
		/* Set a timeout to re-add the PollFD to the source */
		g_source_ref (source);
		g_timeout_add (TIMEOUT_MILLISECONDS, ik_source_timeout, source);

		return FALSE;
	}

do_read:
	/* We are ready to read events from inotify */

	prev_pending = 0;
	pending_count = 0;

	return TRUE;
}

static gboolean
ik_source_dispatch (GSource *source,
		    GSourceFunc callback,
		    gpointer user_data)
{
	if (callback)
	{
		return callback(user_data);
	}
	return TRUE;
}

GSourceFuncs ik_source_funcs =
{
	ik_source_prepare,
	ik_source_check,
	ik_source_dispatch,
	NULL
};

gboolean ik_startup (void (*cb)(ik_event_t *event))
{
	static gboolean initialized = FALSE;
	GSource *source;

	user_cb = cb;
	/* Ignore multi-calls */
	if (initialized) {
		return inotify_instance_fd >= 0;
	}

	initialized = TRUE;
	inotify_instance_fd = inotify_init ();

	if (inotify_instance_fd < 0) {
		return FALSE;
	}

	inotify_read_ioc = g_io_channel_unix_new(inotify_instance_fd);
	ik_poll_fd.fd = inotify_instance_fd;
	ik_poll_fd.events = G_IO_IN | G_IO_HUP | G_IO_ERR;
	g_io_channel_set_encoding(inotify_read_ioc, NULL, NULL);
	g_io_channel_set_flags(inotify_read_ioc, G_IO_FLAG_NONBLOCK, NULL);

	source = g_source_new (&ik_source_funcs, sizeof(GSource));
	g_source_add_poll (source, &ik_poll_fd);
	g_source_set_callback(source, ik_read_callback, NULL, NULL);
	g_source_attach(source, NULL);
	g_source_unref (source);

	cookie_hash = g_hash_table_new(g_direct_hash, g_direct_equal);
	event_queue = g_queue_new ();
	events_to_process = g_queue_new ();

	return TRUE;
}

static ik_event_internal_t *ik_event_internal_new (ik_event_t *event)
{
	ik_event_internal_t *internal_event = g_new0(ik_event_internal_t, 1);
	GTimeVal tv;

	g_assert (event);
	
	g_get_current_time (&tv);
	g_time_val_add (&tv, DEFAULT_HOLD_UNTIL_TIME);
	internal_event->event = event;
	internal_event->hold_until = tv;

	return internal_event;
}

static ik_event_t *ik_event_new (char *buffer)
{
   struct inotify_event *kevent = (struct inotify_event *)buffer;
   g_assert (buffer);
   ik_event_t *event = g_new0(ik_event_t,1);
   event->wd = kevent->wd;
   event->mask = kevent->mask;
   event->cookie = kevent->cookie;
   event->len = kevent->len;
   if (event->len)
      event->name = g_strdup(kevent->name);
   else
      event->name = g_strdup("");

   return event;
}

ik_event_t *ik_event_new_dummy (const char *name, gint32 wd, guint32 mask)
{
	ik_event_t *event = g_new0(ik_event_t,1);
	event->wd = wd;
	event->mask = mask;
	event->cookie = 0;
	if (name)
		event->name = g_strdup(name);
	else
		event->name = g_strdup("");

	event->len = strlen (event->name);

	return event;
}

void ik_event_free (ik_event_t *event)
{
	if (event->pair)
		ik_event_free (event->pair);
	g_free(event->name);
	g_free(event);
}

gint32 ik_watch (const char *path, guint32 mask, int *err)
{
   gint32 wd = -1;

   g_assert (path != NULL);
   g_assert (inotify_instance_fd >= 0);

   wd = inotify_add_watch (inotify_instance_fd, path, mask);

   if (wd < 0)
   {
      int e = errno;
      // FIXME: debug msg failed to add watch
      if (err)
         *err = e;
      return wd;
   }

   g_assert (wd >= 0);
   return wd;
}

int ik_ignore(const char *path, gint32 wd)
{
	g_assert (wd >= 0);
	g_assert (inotify_instance_fd >= 0);

	if (inotify_rm_watch (inotify_instance_fd, wd) < 0)
	{
		//int e = errno;
		// failed to rm watch
		return -1;
	}

	return 0;
}

void ik_move_stats (guint32 *matches, guint32 *misses)
{
	if (matches)
		*matches = ik_move_matches;

	if (misses)
		*misses = ik_move_misses;
}

const char *ik_mask_to_string (guint32 mask)
{
	gboolean is_dir = mask & IN_ISDIR;
	mask &= ~IN_ISDIR;

	if (is_dir)
	{
		switch (mask)
		{
			case IN_ACCESS:
				return "ACCESS (dir)";
			break;
			case IN_MODIFY:
				return "MODIFY (dir)";
			break;
			case IN_ATTRIB:
				return "ATTRIB (dir)";
			break;
			case IN_CLOSE_WRITE:
				return "CLOSE_WRITE (dir)";
			break;
			case IN_CLOSE_NOWRITE:
				return "CLOSE_NOWRITE (dir)"; 
			break;
			case IN_OPEN:
				return "OPEN (dir)";
			break;
			case IN_MOVED_FROM:
				return "MOVED_FROM (dir)";
			break;
			case IN_MOVED_TO:
				return "MOVED_TO (dir)";
			break;
			case IN_DELETE:
				return "DELETE (dir)";
			break;
			case IN_CREATE:
				return "CREATE (dir)";
			break;
			case IN_DELETE_SELF:
				return "DELETE_SELF (dir)";
			break;
			case IN_UNMOUNT:
				return "UNMOUNT (dir)";
			break;
			case IN_Q_OVERFLOW:
				return "Q_OVERFLOW (dir)";
			break;
			case IN_IGNORED:
				return "IGNORED (dir)";
			break;
			default:
				return "UNKNOWN_EVENT (dir)";
			break;

		}
	} else {
		switch (mask)
		{
			case IN_ACCESS:
				return "ACCESS";
			break;
			case IN_MODIFY:
				return "MODIFY";
			break;
			case IN_ATTRIB:
				return "ATTRIB";
			break;
			case IN_CLOSE_WRITE:
				return "CLOSE_WRITE";
			break;
			case IN_CLOSE_NOWRITE:
				return "CLOSE_NOWRITE";
			break;
			case IN_OPEN:
				return "OPEN";
			break;
			case IN_MOVED_FROM:
				return "MOVED_FROM";
			break;
			case IN_MOVED_TO:
				return "MOVED_TO";
			break;
			case IN_DELETE:
				return "DELETE";
			break;
			case IN_CREATE:
				return "CREATE";
			break;
			case IN_DELETE_SELF:
				return "DELETE_SELF";
			break;
			case IN_UNMOUNT:
				return "UNMOUNT";
			break;
			case IN_Q_OVERFLOW:
				return "Q_OVERFLOW";
			break;
			case IN_IGNORED:
				return "IGNORED";
			break;
			default:
				return "UNKNOWN_EVENT";
			break;

		}
	}
}


static void ik_read_events (gsize *buffer_size_out, gchar **buffer_out)
{
	static gchar *buffer = NULL;
	static gsize buffer_size;

	/* Initialize the buffer on our first call */
	if (buffer == NULL)
	{
		buffer_size = AVERAGE_EVENT_SIZE;
		buffer_size *= MAX_QUEUED_EVENTS;
		buffer = g_malloc (buffer_size);

		if (!buffer) {
			*buffer_size_out = 0;
			*buffer_out = NULL;
			return;
		}
	}

	*buffer_size_out = 0;
	*buffer_out = NULL;

	memset(buffer, 0, buffer_size);

	if (g_io_channel_read_chars (inotify_read_ioc, (char *)buffer, buffer_size, buffer_size_out, NULL) != G_IO_STATUS_NORMAL) {
		// error reading
	}
	*buffer_out = buffer;
}

static gboolean ik_read_callback(gpointer user_data)
{
	gchar *buffer;
	gsize buffer_size, buffer_i, events;

	G_LOCK(inotify_lock);
	ik_read_events (&buffer_size, &buffer);

	buffer_i = 0;
	events = 0;
	while (buffer_i < buffer_size)
	{
		struct inotify_event *event;
		gsize event_size;
		event = (struct inotify_event *)&buffer[buffer_i];
		event_size = sizeof(struct inotify_event) + event->len;
		g_queue_push_tail (events_to_process, ik_event_internal_new (ik_event_new (&buffer[buffer_i])));
		buffer_i += event_size;
		events++;
	}

	/* If the event process callback is off, turn it back on */
	if (!process_eq_running && events)
	{
		process_eq_running = TRUE;
		g_timeout_add (PROCESS_EVENTS_TIME, ik_process_eq_callback, NULL);
	}

	G_UNLOCK(inotify_lock);
	return TRUE;
}

static gboolean
g_timeval_lt(GTimeVal *val1, GTimeVal *val2)
{
	if (val1->tv_sec < val2->tv_sec)
		return TRUE;

	if (val1->tv_sec > val2->tv_sec)
		return FALSE;

	/* val1->tv_sec == val2->tv_sec */
	if (val1->tv_usec < val2->tv_usec)
		return TRUE;

	return FALSE;
}

static gboolean
g_timeval_eq(GTimeVal *val1, GTimeVal *val2)
{
	return (val1->tv_sec == val2->tv_sec) && (val1->tv_usec == val2->tv_usec);
}

static void
ik_pair_events (ik_event_internal_t *event1, ik_event_internal_t *event2)
{
	g_assert (event1 && event2);
	/* We should only be pairing events that have the same cookie */
	g_assert (event1->event->cookie == event2->event->cookie);
	/* We shouldn't pair an event that already is paired */
	g_assert (event1->pair == NULL && event2->pair == NULL);

	/* Pair the internal structures and the ik_event_t structures */
	event1->pair = event2;
	event1->event->pair = event2->event;

	if (g_timeval_lt (&event1->hold_until, &event2->hold_until))
		event1->hold_until = event2->hold_until;

	event2->hold_until = event1->hold_until;
}

static void
ik_event_add_microseconds (ik_event_internal_t *event, glong ms)
{
	g_assert (event);
	g_time_val_add (&event->hold_until, ms);
}

static gboolean
ik_event_ready (ik_event_internal_t *event)
{
	GTimeVal tv;
	g_assert (event);

	g_get_current_time (&tv);

	/* An event is ready if,
	*
	* it has no cookie -- there is nothing to be gained by holding it
	* or, it is already paired -- we don't need to hold it anymore
	* or, we have held it long enough
	*/
	return event->event->cookie == 0 ||
	       event->pair != NULL ||
	       g_timeval_lt(&event->hold_until, &tv) || g_timeval_eq(&event->hold_until, &tv);
}

static void
ik_pair_moves (gpointer data, gpointer user_data)
{
	ik_event_internal_t *event = (ik_event_internal_t *)data;

	if (event->seen == TRUE || event->sent == TRUE)
	return;

	if (event->event->cookie != 0)
	{
		/* When we get a MOVED_FROM event we delay sending the event by
		* MOVE_HOLD_UNTIL_TIME microseconds. We need to do this because a
		* MOVED_TO pair _might_ be coming in the near future */
		if (event->event->mask & IN_MOVED_FROM) {
			g_hash_table_insert (cookie_hash, GINT_TO_POINTER(event->event->cookie), event);
			// because we don't deliver move events there is no point in waiting for the match right now.
			ik_event_add_microseconds (event, MOVE_HOLD_UNTIL_TIME);
		} else if (event->event->mask & IN_MOVED_TO) {
			/* We need to check if we are waiting for this MOVED_TO events cookie to pair it with
			* a MOVED_FROM */
			ik_event_internal_t *match = NULL;
			match = g_hash_table_lookup (cookie_hash, GINT_TO_POINTER(event->event->cookie));
			if (match) {
				g_hash_table_remove (cookie_hash, GINT_TO_POINTER(event->event->cookie));
				ik_pair_events (match, event);
			}
		}
	}
	event->seen = TRUE;
}

static void
ik_process_events ()
{
	g_queue_foreach (events_to_process, ik_pair_moves, NULL);

	while (!g_queue_is_empty (events_to_process))
	{
		ik_event_internal_t *event = g_queue_peek_head (events_to_process);

		/* This must have been sent as part of a MOVED_TO/MOVED_FROM */
		if (event->sent)
		{
			/* Pop event */
			g_queue_pop_head (events_to_process);
			/* Free the internal event structure */
			g_free (event);
			continue;
		}

		/* The event isn't ready yet */
		if (!ik_event_ready (event)) {
			break;
		}

		/* Pop it */
		event = g_queue_pop_head (events_to_process);

		/* Check if this is a MOVED_FROM that is also sitting in the cookie_hash */
		if (event->event->cookie && event->pair == NULL &&
		    g_hash_table_lookup (cookie_hash, GINT_TO_POINTER(event->event->cookie)))
		{
			g_hash_table_remove (cookie_hash, GINT_TO_POINTER(event->event->cookie));
		}

		if (event->pair) {
			/* We send out paired MOVED_FROM/MOVED_TO events in the same event buffer */
			//g_assert (event->event->mask == IN_MOVED_FROM && event->pair->event->mask == IN_MOVED_TO);
			/* Copy the paired data */
			event->pair->sent = TRUE;
			event->sent = TRUE;
			ik_move_matches++;
		} else if (event->event->cookie) {
			/* If we couldn't pair a MOVED_FROM and MOVED_TO together, we change
			* the event masks */
			/* Changeing MOVED_FROM to DELETE and MOVED_TO to create lets us make
			* the gaurantee that you will never see a non-matched MOVE event */

			if (event->event->mask & IN_MOVED_FROM) {
				event->event->mask = IN_DELETE|(event->event->mask & IN_ISDIR);
				ik_move_misses++; // not super accurate, if we aren't watching the destination it still counts as a miss
			}
			if (event->event->mask & IN_MOVED_TO)
				event->event->mask = IN_CREATE|(event->event->mask & IN_ISDIR);
		}

		/* Push the ik_event_t onto the event queue */
		g_queue_push_tail (event_queue, event->event);
		/* Free the internal event structure */
		g_free (event);
	}
}

gboolean ik_process_eq_callback (gpointer user_data)
{
    /* Try and move as many events to the event queue */
	G_LOCK(inotify_lock);
	ik_process_events ();

	while (!g_queue_is_empty (event_queue))
	{
		ik_event_t *event = g_queue_pop_head (event_queue);

		user_cb (event);
	}

	if (g_queue_get_length (events_to_process) == 0)
	{
		process_eq_running = FALSE;
		G_UNLOCK(inotify_lock);
		return FALSE;
	} else {
		G_UNLOCK(inotify_lock);
		return TRUE;
	}
}
